In display panels of the active matrix type, e.g., liquid crystal panels, etc., there is the trend where the number of pixels is increased with realization of high definition devices (display panels). In the case where the number of pixels is increased in such a way, since write time becomes short in dot sequential drive system where video signals are written by one pixel, there is employed a plural pixel simultaneous sampling system in which plural video signal input lines for delivering video signals from the external to the liquid crystal are provided to simultaneously perform sampling of video signals delivered from the plural video signal input lines to deliver the video signals thus sampled to plural pixels.
When the liquid crystal panel is caused to be driven by the plural pixel simultaneous sampling system, it is possible to obtain sufficient write time of video signal. Accordingly, in display panels of increased pixel number, i.e., relatively high definition active matrix type such as XGA (eXtended Graphic Array: 1024×768), WXGA (Wide eXtended Graphic Array: 1386×768), or SXGA (Super eXtended Graphic Array: 1400×1500), and display panels of increased pixel number, i.e., high definition active matrix type such as SXGA+(Super eXtended Graphic Array PLUS : 1400×1050), UXGA (Ultra eXtended Graphic Array: 1600×1200), Full HD (Full High Definition: 1920×1080), the plural pixel simultaneous sampling system is employed so that write operation of video signals can be satisfactorily executed.
The plural pixel simultaneous sampling system for driving the liquid crystal panel will be explained by using FIGS. 1 and 2.
FIG. 1 is a liquid crystal drive system 50 mounted in a liquid crystal projector, which comprises liquid crystal panels 60R, 60B, 60G which are respectively liquid crystal panel for red, liquid crystal panel for green and liquid crystal panel for blue driven by the plural pixel simultaneous sampling system.
The respective liquid crystal panels 60R, 60C, 60B that the liquid crystal panel drive system 50 has are a liquid crystal panel complying with the XGA format, wherein video signals are simultaneously written by 6 (six) pixels with respect to pixels in a horizontal direction by the plural pixel simultaneous sampling system.
The liquid crystal panel drive system 50 comprises a DSD (Digital Signal Driver) 51 including a DSD core 51a for implementing gamma correction and/or color unevenness correction, etc. to digital video signals for red (R), digital video signals for green (G) and digital video signal for blue (B) which are delivered from the external, and LCD drivers 52, 53, 54 for converging digital video signals which have been caused to undergo correction processing by the DSD 51 into analog video signals to deliver the analog video signals thus obtained to the respective liquid crystal panels 60R, 60B, 60G. The respective liquid crystal panels 60R, 60B, 60G are respectively mounted at liquid crystal panel modules 61R, 61G, 61B along with horizontal drive circuit and vertical drive circuits which are not shown.
The LCD drivers 51, 52, 53 serve to convert digital video signals delivered from the DSD 51 into analog video signals of which number corresponds to the number of sampling for performing simultaneous sampling of digital video signals delivered from the DSD 51. At the liquid crystal panels 60R, 60G, 60B which comply with the XGA format, since the number of simultaneous sampling operations is set to six (pixels), the LCD drivers 52, 53, 54 serve to convert digital video signals delivered into six parallel analog video signals.
It is to be noted that timing pulses for driving the respective liquid panels 60R, 60G, 60B are generated by a TG (Timing Generator) 51b of the DSD 51.
Subsequently, the plural pixel simultaneous sampling system will be explained in detail by using the liquid crystal panel module 61R shown in FIG. 2. It is to be noted that since plural pixel simultaneous sampling systems at liquid crystal panels 60R, 60G, 60B are entirely the same, explanation will be given by using, as representative, the liquid crystal panel module 61R on which liquid crystal panel 60R is mounted.
As shown in FIG. 2, the liquid crystal panel module 61R is supplied, through video signal supply lines VSIGI to VSIG6, six parallel analog signals which have been converted at the LCD driver 52.
The liquid crystal panel module 61R comprises groups of sampling switches SWN each comprised of six sampling switches for simultaneously performing sampling of six signal lines 63 among signal lines 63 that the liquid crystal panel 60R has.
The groups of sampling switches are driven in order of groups of sampling switches SW1, SW2, . . . , SWN-1, and SWN in accordance with switch pulses delivered from a horizontal drive circuit 62. Thus, at the signal lines 63, video signals are simultaneously sampled in units of six video signals. As a result, video signals are written into pixels 64 in the row direction selected by vertical drive circuits (not shown).
Since it is necessary to sufficiently ensure write time of video signal in general, it is necessary that according as resolution of the liquid crystal panel becomes higher, it is required to increase the number of pixels to be simultaneously sampled by taking the transistor characteristic and/or the switch characteristic of the liquid crystal panel, etc. into consideration. For example, in the SXGA, it is necessary that the number of pixels subject to simultaneous sampling is set to 12 (pixels). In the UXGA, it is necessary that the number of pixels subject to simultaneous sampling is set to 24 (pixels).
As stated above, in the conventional plural pixel simultaneous sampling system, since it is necessary to change the number of pixels subject to simultaneous sampling in accordance with difference of the display format of the liquid crystal panel, it is required to also change the number of video signals delivered to the liquid crystal panel, i.e., the number of parallel analog video signals converted at the LCD drivers 52, 53, 54 in FIGS. 1 and 2 in accordance with the display format.
Accordingly, in order that the liquid crystal panel drive system 50 is caused to comply with liquid crystal panels of various display formats, LCD drivers 52, 53, 54 are required by the number of display formats. As a result, there would take place the problem that the cost is increased, and/or the apparatus becomes large-sized.
In addition, in the plural pixel simultaneous sampling system, there is the problem that there would take place ghost which is the phenomenon that the same image is displayed in the state shifted in a manner to overlap from image primarily displayed by the phase relationship between video signal and timing pulse.